Induction of gynogenesis with ultra-violet irradiated Koi carp (Cyprinus carpio haematopterus) sperm demonstrates the XX/XY sex determination system in Opsariichthys bidens

Abstract

Opsariichthys bidens (Chinese hooksnout carp) is a small stream fish with high economic value. As the males of this species grow faster than females, it follows that mono-sex breeding has significant potential for commercial production. However, little is known about the sex determination system in O. bidens, this is the key process that is used to develop mono-sex breeding in fish. In the present study, we induced gynogenesis by fertilizing O.bidens eggs with ultra-violet (UV)- inactivated Cyprinus carpio haematopterus (Koi carp) sperm followed by cold shock treatment. Results showed that the optimal induction conditions was 25 min duration of cold shock treatment at 2 min post fertilization (mpf), the highest fertilization rate and hatching rate for gynogenic embryos were 68.24 ± 3.75% and 12.54 ± 1.59%, respectively. Embryos derived from gynogenesis developed normally, but the hybrid embryos failed (created with non-UV-inactivated Koi carp sperm and O.bidens eggs). Genetic analysis demonstrated only maternal inheritance in the gynogenetic offspring. Histological analysis further showed that the gonads of all gynogenetic fish were ovaries, thus suggesting that the sex-determining system of O. bidens is male heterogametic (XX-XY). The present study is the first to establish a procedure for inducing gynogenesis, we also identified the sex determination system (SD) of O. bidens, that will be possible to produce only male.